A. Technical Field
The present invention relates to a block copolymer which displays excellent performance such as dispersibility, and to a production process for the block copolymer, and uses of the block copolymer.
B. Background Art
Hitherto, a polyether block copolymer is known which has structural units derived from ethylene- and propylene oxides respectively. Such a block polymer has surface activity. However, when used as a pigment dispersant, it does not display satisfactory performance. In addition, when used as a water-treating agent, it does not display satisfactory scale inhibitability, either, and when used for trapping hardness components in water or used as a mud dirt dispersant, it does not provide any satisfactory results, either.
As to a polymer having both structural units derived from an alkylene oxide and a carboxylic acid, U.S. Pat. No. 4,204,052 discloses a random copolymer having structural units derived from ethylene oxide and a glyoxylic acid derivative respectively. In addition, U.S. Pat. No. 4,144,226 discloses a polymer of glyoxylic acid, of which both terminal moieties are ethylene glycol monoether derivative ones as obtained by reacting 1 to 3 molecules of ethylene oxide upon both terminal moieties of a polymer molecule for stabilization. These U.S. patents both disclose that polymers, as disclosed therein, are used as detergent builders.
In the random copolymer as disclosed in U.S. Pat. No. 4,204,052, carboxylate ions are arranged on the polymer at random. For example, in the case where this polymer is used as a cement dispersant, it has negative charges to the same extent at any polymer side chain moiety and is therefore adsorbed to cement particles almost homogeneously. Thus, polymer moieties that are not adsorbed to cement particles are considered few, so it cannot be expected to effectively disperse cement particles utilizing steric repulsion between these polymer moieties that are not adsorbed to cement particles. In addition, in the case where the homopolymers as disclosed in U.S. Pat. No. 4,144,226 are used as a cement dispersant, the contribution of the terminal alkylene oxide moiety of this polymer is so small that this polymer is adsorbed strongly to cement particles that have positive charges, and therefore it cannot be expected to effectively disperse cement particles, either. Accordingly, the polymers as disclosed in the above-mentioned U.S. patents may have satisfactory performance as builders, but are not sufficient with regard to the dispersibility, because many carboxylate ions are arranged on the polymers.
In addition, none of the polymers as disclosed in the above-mentioned U.S. patents has a series of alkylene oxide groups. Therefore, when used as detergent builders, these polymers only display insufficient dispersibility, low washability, and inferior biodegradability.